1. Field of the Invention
This invention relates to an automatic universal head which supports a camera or the like and can automatically rotate the camera or the like in any direction by remote operation and can position the camera or the like as desired, and more particularly to an automatic universal head improved in the control circuit thereof.
2. Related Background Art
An automatic universal head on which a camera or the like is mounted and which can automatically rotate the camera or the like in any direction by remote operation and can position the camera or the like is known.
Heretofore, in this known automatic universal head, a control circuit as shown in FIG. 3 of the accompanying drawings (i.e., a position servo mechanism) has been provided for a motor for rotating the universal head. In FIG. 3, reference numeral 1 designates a motor driving circuit for controlling the voltage and current of the motor M, reference numeral 2 denotes a position detector such as a potentiometer which generates a position detection signal corresponding to the rotated position (the angle of rotation) of the universal head (not shown), reference numeral 3 designates a position instruction signal generator which generates a position instruction signal for rotating the universal head to any rotated position, and reference numeral 4 denotes a position difference signal detector which generates the difference between the output signal of the position detector 2 and the position instruction signal (i.e., the position difference signal) as an output signal and controls the motor driving circuit 1.
In the conventional automatic universal head having the control circuit as described above, the applied voltage and supplied current to the motor M are controlled by the difference between the output signal of the position detector 2 and the position instruction signal (i.e., the position difference detection signal) and therefore, when the motor M is started (that is, when the universal head is started), the difference between the position instruction signal and the output signal of the position detector 2 becomes greatest and thus, a great applied voltage and a great current are supplied to the motor M, which is thus started with the maximum torque thereof.
Now, in the automatic universal head as described above, if extraneous tension is applied to the camera cable of a camera mounted on the universal head or if a telephoto lens is mounted on the camera and the center of composite gravity of the camera and the telephoto lens is not coincident with the tilt rotation axis, the load torque of the universal head will become remarkably great. Furthermore even if a position instruction signal is put out from the position instruction signal generator 3, the motor M for rotating the universal head will not be started and there may occur a situation in which said great voltage and said great current continue to be applied to the field winding and armature winding of the motor M. If the automatic universal head is remote-operated, the operator is far from the universal head and therefore, even if such a situation occurs, the operator often cannot cope with the situation quickly and accordingly, an accident such as the motor burning up is possible.
However, in the conventional automatic universal head as described above, there is no function of preventing the occurrence of the situation as previously described and thus, in the case as described above, there has been the danger of the motor being burnt up.